With steadily growing case rates of cancer, which is classified as one of three major diseases in Japan, there are strong desires for useful methods for early diagnosis and treatment thereof. Research and development has actively been advancing, in particular, for medical image diagnostic apparatuses that afford quite an early discovery and identification of cancers. Advances in technology are marked in multiple modalities, including positron emission tomography (PET), Computed Tomography (CT), and magnetic resonance imaging (MRI), and ultrasonic wave. However, even with an early discovery, surgical operations and radiation treatments involve high risks and adverse reactions. Therefore, there are some cases where it is difficult to determine to embark on the treatment. For this reason, research and development is imperative of a method for minimally-invasive therapy, which accommodates to the early discovery.
One such advancing research for minimally-invasive therapies is of an embolization therapy. An embolization therapy is a method for treatment, which yields a treatment effect by necrotizing localized diseases, i.e. an original tumor, a hysteromyoma, and so on, by blocking nutrient vessels. More specifically, there is used a method for occluding a blood vessel, in which a catheter is inserted to a nutrient vessel of a tumor to inject an embolic agent thereinto under X-ray monitoring.
However, this method of treatment involves possibility that the embolic agent causes occlusion of blood vessels connecting to normal tissues, and there is always the risk that the normal tissues are also necrotized. Moreover, due to the usage of catheter, this treatment requires to be performed under local or general anesthesia of the patient. Moreover, it has been pointed out that this method for treatment is not necessarily minimally invasive since it uses X-ray for monitoring.
Then, in order to achieve less invasivity of the embolization therapy, various methods have been developed from respective viewpoints of monitoring, embolic agents and transfer techniques. First, a method has been reported that uses bubbles, not a solid substance, as an embolic agent (Patent Literature 1). In this method, monitoring can be performed by using ultrasonic wave, instead of X-ray, and therefore reduction of exposure to X-ray is expected. Further, Patent Literature 2 discloses a method in which a liquid medical agent is administered in a biological body in advance, and external stimulus is applied to a target position to cause the medical agent to form into bubbles, thereby blocking the blood flow to and from a tumor. Further, Patent Literature 3 discloses a method in which insertion of embolic agent using a catheter is not used, i.e. a method that blocks blood flow by applying focused ultrasonic wave to a target blood vessel and denaturing the blood vessel. Furthermore, Patent Literature 4 discloses a method in which bubbles are locally formed by using ultrasonic wave energy, and the generated bubbles are used to implement the embolization therapy.
However, all of the above-stated methods for minimally-invasive embolization therapy have problems in certainty of the treatment. For example, in the method using bubbles, it is difficult to achieve the effect of occlusion unless considerable amount of bubbles are stably supplied into the blood vessels to embolize them, because, while the size of a micro bubble used in this method is no greater than 1-5 μm or so, the diameters of capillary vessels in a tumor are 10-40 μm and, moreover, the diameter of major arterial vessels connecting to the tumor is 1 mm or greater. Administration of a material to form into bubbles into a biological body in advance has the same problem in principle. Further, also in the case of applying ultrasonic wave energy to a target blood vessel in order to denature the blood vessel, it is difficult to unfailingly denature a solely one blood vessel, because dislocation is likely to occur between a position where the ultrasonic wave energy converges and a position of a geometric focus of a transducer, due to the effect of attenuation of the ultrasonic wave within the biological body.